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Yes, you can do that, you can even buy transistors with more closely defined hFE. For example, the 2SC1815Y is guaranteed to have an hFE within a 2:1 range (120~240). It might vary another 2:1 from -25°C to 100°C, so that's a 4:1 range total, plus perhaps 50% for Vce variation. In SMT, the BCX70x is even more tightly specified (< 2:1 at 2mA).

It's generally frowned upon by folks who have never done the math, but it will work if you're not that picky (5-6:1). Expect a lot of clucking. This crappy method of biasing transistors has been used in consumer electronics in the past many times.

The JFET regulator diode probably won't work because the 1.2V is too low to get it to regulate well.

Using a dual transistor (eg. MBT3904) with the below circuit gives you a lot better control. It's best to use a dual so they will track thermally. The current will probably change 10-15% over temperature (simulate it if that matters to you). I did the below for 2mA nominal. The self-heating will cause the current to increase somewhat over time, depending on the voltage, but it still should be pretty good.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

Yes, you can do that, you can even buy transistors with more closely defined hFE. For example, the 2SC1815Y is guaranteed to have an hFE within a 2:1 range (120~240). It might vary another 2:1 from -25°C to 100°C, so that's a 4:1 range total, plus perhaps 50% for Vce variation. In SMT, the BCX70x is even more tightly specified (< 2:1 at 2mA).

It's generally frowned upon by folks who have never done the math, but it will work if you're not that picky (5-6:1). Expect a lot of clucking. This crappy method of biasing transistors has been used in consumer electronics in the past many times.

The JFET regulator diode probably won't work because the 1.2V is too low to get it to regulate well.

Using a dual transistor with the below circuit gives you a lot better control. It's best to use a dual so they will track thermally. The current will probably change 10-15% over temperature (simulate it if that matters to you). I did the below for 2mA nominal. The self-heating will cause the current to increase somewhat over time, depending on the voltage, but it still should be pretty good.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

Yes, you can do that, you can even buy transistors with more closely defined hFE. For example, the 2SC1815Y is guaranteed to have an hFE within a 2:1 range (120~240). It might vary another 2:1 from -25°C to 100°C, so that's a 4:1 range total, plus perhaps 50% for Vce variation. In SMT, the BCX70x is even more tightly specified (< 2:1 at 2mA).

It's generally frowned upon by folks who have never done the math, but it will work if you're not that picky (5-6:1). Expect a lot of clucking. This crappy method of biasing transistors has been used in consumer electronics in the past many times.

The JFET regulator diode probably won't work because the 1.2V is too low to get it to regulate well.

Using a dual transistor (eg. MBT3904) with the below circuit gives you a lot better control. It's best to use a dual so they will track thermally. The current will probably change 10-15% over temperature (simulate it if that matters to you). I did the below for 2mA nominal. The self-heating will cause the current to increase somewhat over time, depending on the voltage, but it still should be pretty good.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

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Yes, you can do that, you can even buy transistors with more closely defined hFE. For example, the 2SC1815Y is guaranteed to have an hFE within a 2:1 range (120~240). It might vary another 2:1 from -25°C to 100°C, so that's a 4:1 range total, plus perhaps 50% for Vce variation. In SMT, the BCX70x is even more tightly specified (< 2:1 at 2mA).

It's generally frowned upon by folks who have never done the math, but it will work if you're not that picky (5-6:1). Expect a lot of clucking. This crappy method of biasing transistors has been used in consumer electronics in the past many times.

The JFET regulator diode probably won't work because the 1.2V is too low to get it to regulate well.

Using a dual transistor with the below circuit gives you a lot better control. It's best to use a dual so they will track thermally. The current will probably change 10-15% over temperature (simulate it if that matters to you). I did the below for 2mA nominal. The self-heating will cause the current to increase somewhat over time, depending on the voltage, but it still should be pretty good.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

Yes, you can do that, you can even buy transistors with more closely defined hFE. For example, the 2SC1815Y is guaranteed to have an hFE within a 2:1 range (120~240). It might vary another 2:1 from -25°C to 100°C, so that's a 4:1 range total, plus perhaps 50% for Vce variation.

It's generally frowned upon by folks who have never done the math, but it will work if you're not that picky (5-6:1). Expect a lot of clucking. This crappy method of biasing transistors has been used in consumer electronics in the past many times.

The JFET regulator diode probably won't work because the 1.2V is too low to get it to regulate well.

Using a dual transistor with the below circuit gives you a lot better control. It's best to use a dual so they will track thermally. The current will probably change 10-15% over temperature (simulate it if that matters to you). I did the below for 2mA nominal. The self-heating will cause the current to increase somewhat over time, depending on the voltage, but it still should be pretty good.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

Yes, you can do that, you can even buy transistors with more closely defined hFE. For example, the 2SC1815Y is guaranteed to have an hFE within a 2:1 range (120~240). It might vary another 2:1 from -25°C to 100°C, so that's a 4:1 range total, plus perhaps 50% for Vce variation. In SMT, the BCX70x is even more tightly specified (< 2:1 at 2mA).

It's generally frowned upon by folks who have never done the math, but it will work if you're not that picky (5-6:1). Expect a lot of clucking. This crappy method of biasing transistors has been used in consumer electronics in the past many times.

The JFET regulator diode probably won't work because the 1.2V is too low to get it to regulate well.

Using a dual transistor with the below circuit gives you a lot better control. It's best to use a dual so they will track thermally. The current will probably change 10-15% over temperature (simulate it if that matters to you). I did the below for 2mA nominal. The self-heating will cause the current to increase somewhat over time, depending on the voltage, but it still should be pretty good.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

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Yes, you can do that, you can even buy transistors with more closely defined hFE. For example, the 2SC1815Y is guaranteed to have an hFE within a 2:1 range (120~240). It might vary another 2:1 from -25°C to 100°C, so that's a 4:1 range total, plus perhaps 50% for Vce variation.

It's generally frowned upon by folks who have never done the math, but it will work if you're not that picky (45-6:1). Expect a lot of clucking. This crappy method of biasing transistors has been used in consumer electronics in the past many times.

The JFET regulator diode probably won't work because the 1.2V is too low to get it to regulate well.

Using a dual transistor with the below circuit gives you a lot better control. It's best to use a dual so they will track thermally. The current will probably change 10-15% over temperature (simulate it if that matters to you). I did the below for 2mA nominal. The self-heating will cause the current to increase somewhat over time, depending on the voltage, but it still should be pretty good.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

Yes, you can do that, you can even buy transistors with more closely defined hFE. For example, the 2SC1815Y is guaranteed to have an hFE within a 2:1 range (120~240). It might vary another 2:1 from -25°C to 100°C, so that's a 4:1 range total.

It's generally frowned upon by folks who have never done the math, but it will work if you're not that picky (4:1). Expect a lot of clucking.

The JFET regulator diode probably won't work because the 1.2V is too low to get it to regulate.

Using a dual transistor with the below circuit gives you a lot better control. It's best to use a dual so they will track thermally. The current will probably change 10-15% over temperature (simulate it if that matters to you). I did the below for 2mA nominal. The self-heating will cause the current to increase somewhat over time, depending on the voltage, but it still should be pretty good.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

Yes, you can do that, you can even buy transistors with more closely defined hFE. For example, the 2SC1815Y is guaranteed to have an hFE within a 2:1 range (120~240). It might vary another 2:1 from -25°C to 100°C, so that's a 4:1 range total, plus perhaps 50% for Vce variation.

It's generally frowned upon by folks who have never done the math, but it will work if you're not that picky (5-6:1). Expect a lot of clucking. This crappy method of biasing transistors has been used in consumer electronics in the past many times.

The JFET regulator diode probably won't work because the 1.2V is too low to get it to regulate well.

Using a dual transistor with the below circuit gives you a lot better control. It's best to use a dual so they will track thermally. The current will probably change 10-15% over temperature (simulate it if that matters to you). I did the below for 2mA nominal. The self-heating will cause the current to increase somewhat over time, depending on the voltage, but it still should be pretty good.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

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