# Which transistor ratings do I use when calculating something?

Let's say I want to calculate VBE for a transistor (for example). What do I use? VCE (Blocked) or VCE (Saturation) or VCE (max)?

Let's say I want to calculate Ic/Ib, what do I use? Ic/Ib (blocked) or Ic/Ib (Sat) or Ic/Ib (max)?

Let's say I want to calculate VCE, what do I use? VBE (Blocked) or VBE (Sat) or VBE (max)?

If I was given a chart or a table like this:

but with more (stuffmax or stuffsat) and stuff like that, what would I use?

I'm so confused.

• Please share the schematic of the circuit where you’re applying the transistor. – The Photon Sep 9 '20 at 15:39
• That appears to be the Absolute Maximum Ratings table. For actual operation you should look at the Electrical Charicteristics table. – Peter Bennett Sep 9 '20 at 15:40
• @ThePhoton There is no specific circuit. Just any circuit. Let's say I want to calculate anything, what parameters I use? The "max" or "sat" or "blocked" ones? – TechnoKnight Sep 9 '20 at 15:40
• The Absolute Maximum Ratings are just that - applying voltages or currents beyond the Absolute Maximum rating is likely to damage the device, so you don't want to operate the device near those values. – Peter Bennett Sep 9 '20 at 15:47
• Where did you see "blocked" parameters? That's not a term that is normally used to describe transistors. Please provide a link to a complete datasheet that specifies these parameters. – The Photon Sep 9 '20 at 16:44

There are typically three types of parameters provided on a datasheet:

Absolute Maximum Ratings tell you the maximum or minimum of some parameter, such that if you exceed these limits you may damage the device. For example, if the absolute maximum $$\V_{CE}\$$ is 10 V, then any voltage greater than 10 V applied between the collector and emitter could damage the device.

Electrical Characteristics tell you, given some specified stimulus, how the device will respond. For example, the electrical characteristics table might specify that with $$\I_{C}\$$ of 150 mA and $$\I_B\$$ of 15 mA, $$\V_{CE(sat)}\$$ has a maximum value of 0.3 V.

Recommended Operating Conditions tells you the limits on how you should use the part in order for it to perform as described in the electrical characteristics tables. If you violate the specifications in this table, you cannot count on the electrical characteristics specifications being valid. This section is found more often in datasheets for more complex devices (logic chips, for example) and less often in datasheets for individual devices like transistors.

None of these sections tells you what the voltages (like $$\V_{CE}\$$, $$\V_{BE}\$$, etc.) are in your circuit. Only analyzing the circuit with reference to the device characteristics can tell you that. None of these sections tells you what the currents through the device are in your circuit. Again, you have to analyze the complete circuit to do that.

Let's say I want to calculate Ic/Ib, what do I use? Ic/Ib (blocked) or Ic/Ib (Sat) or Ic/Ib (max)?

1. I've never heard of "Ic/Ib (blocked)"; it isn't an especially widely used way to specify a component.

2. Ic/Ib (sat) basically gives a definition of what this datasheet means when they talk about the saturation operating regime. It doesn't tell you what Ic/Ib is in any situation, it tells you that if Ic/Ib is less than this value, you should consider the other specifications describing the saturation mode to apply.

3. Ic/Ib (max) probably refers to the maximum value you might obtain in forward operating mode. Ideally you should not use this parameter but instead design your circuit as if the transistor current gain could be anywhere between the specified minimum value and infinity. That means, use a feedback mechanism to limit the collector current.

Let's say I want to calculate VCE, what do I use? VBE (Blocked) or VBE (Sat) or VBE (max)?

VBE (blocked): Again, never heard of it.

VBE (Sat): Use this if you are operating in the saturation regime.

VBE (max): This tells you the maximum $$\V_{BE}\$$ you might need to achieve some specified base current. It won't help you calculate $$\V_{CE}\$$ at all.

In the most common single-transistor amplifier configurations, you calculate $$\V_{CE}\$$ by first finding $$\I_C\$$ and then figuring out based on the remainder of the circuit, what $$\V_{CE}\$$ is required to achieve that current. None of the parameters you mentioned are particularly helpful.