54 votes
Accepted

Is there an ideal PWM frequency for DC brush motors?

In short: You have linear control of the 'speed' by applying a PWM signal, now the frequency of that signal has to be high enough so that your DC Motor only passes the DC component of the PWM signal, ...
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  • 5,120
22 votes
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Problems with L293, L298 and SN754410 H-bridge drivers on a low voltage supply

This answer was provided in 2014 and reflects the devices that are available back then. The point of this answer is to demonstrate that there are far better devices around compared to the problematic (...
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  • 384k
19 votes

Is this a case of ground loop?

Not a ground loop. But a short circuit: Always use fuses with batteries. Instead, you can make it like this, so that there is only one common ground: Drawback is unbalanced load on the battery. ...
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  • 20.7k
15 votes

What does the output current rating from an H-Bridge's datasheet really mean?

Recently, I bought the H-Bridge VNH7070BAS from ST because it would drive up to 15A It will not drive anything like this level of current for anything more than a few micro seconds before the ...
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  • 384k
13 votes
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Are Peltier elements polarized?

A TEC is polarized in the sense that how it is connected matters. If you want to be able to heat and cool an element then a full Hbridge will work. This will allow you to pump current both directions ...
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  • 2,328
13 votes

Is there an ideal PWM frequency for DC brush motors?

Your motor is likely geared down, because 150 rpm is only 2.5 revolutions per second. At 50 rpm, your motor will require more than a second to perform one revolution. That having been said, the ...
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13 votes

Why don't flyback diodes in H-bridge damage power supply?

The diodes serve two distinct purposes. Under regenerative braking, they return the generated voltage to the power supply (where with suitable electronics, it can be used to recharge the battery). ...
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12 votes
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Severe ringing when high side MOSFET in half bridge circuit switches on

Try probing on the power supply rail. I bet you see those spikes on there. It'll be due to the lead length between your bench supply and the MOSFETs. Clearly you won't see it on the lower FET side ...
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12 votes
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Why do my P-channel MOSFETs keep dying in this H-bridge?

How are you decoupling the 12V supply? One possible failure mode is that inductive spikes from switching off the motor current (i.e. at the PWM rate) are dumped into the 12V supply via the flyback ...
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11 votes

Why don't flyback diodes in H-bridge damage power supply?

If the motor is producing power, the net power into the motor must be positive, so the net current out of the batteries must be in the direction that drains them, so you are fine. If the motor is ...
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10 votes
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Why is a resistor put before the gate of a transistor?

The reasons are different depending on if it is a BJT or a MOSFET. The effect, though, is the same - it's there to reduce current and protect the IO pins on the controller that are driving the ...
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10 votes

Level shift circuit MCU to MOSFET

I first saw the following circuit in a TI app note many years ago. It works well and is robust. I have used it or variations of it in several projects (and products). simulate this circuit – ...
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  • 22.7k
10 votes

Is there an ideal PWM frequency for DC brush motors?

A practical motor behaves roughly like a resistor and inductor in series with a real motor. For efficient operation you need should switch between connecting the motor to the supply and shorting it ...
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  • 44.5k
10 votes

Can this H-Bridge circuit be used with 12V?

To use this circuit with a 12V supply R5 & R6 must be rated for at least 0.25W power and the 100 ohm resistors must be rated for at least 2W power. Depending on the transistors used these 4 ...
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10 votes
Accepted

Why does my MIC4605 keep blowing up?

On your layout the decoupling cap (finger-painted red) is very far away from the chip, there is a 5R resistor in series (purple) and the current loop area (highlighted in yellow) is quite large. This ...
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10 votes
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H- bridge requirements

I'm wondering, if in a basic H-bridge, the n, and p type fets need to be the same size, current handling wise. No, they don't need to be the same size. They all need to be sufficiently large to ...
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  • 142k
9 votes
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Why use a N channel MOSFET as high side H bridge switches?

P-channel MOSFETs tend to have a higher Rds(on), making them less efficient (for the same price). For a small H-bridge, the simplicity of using them makes them practical However, for high power ...
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9 votes

MOSFET's getting too much heat up without any load

Your P channel MOSFETs are connected upside down: - Notice the little diode symbols inside the MOSFETs? They will permanently conduct current and the MOSFETs will not switch off.
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  • 384k
9 votes

Problem with the L298 datasheet

Those old bipolar processes could only be used to make crummy lateral PNP transistors with quite low gain so not very good for high current. Using all NPN, especially those NPN, transistors is bad (...
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8 votes
Accepted

Only spikes in H-Bridge

Your o-scope time base is set to 1.00 seconds and, by the looks of it your control signals will be switching at 0.5 Hz. This is waaaaaaaaaaay too low in frequency. You have (in your driver circuit) ...
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  • 384k
7 votes
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Level shift circuit MCU to MOSFET

I suggest something more like this: simulate this circuit – Schematic created using CircuitLab Drive into a 10nF load looks like this: Edit: The violet trace is your circuit- as you can see,...
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7 votes

Can this H-Bridge circuit be used with 12V?

That circuit is a disaster. Run away! Analyze what happens with Vcc = 12 V and both switches open. Let's say the B-E junctions of the transistors drop 700 mV. We only need to analyze what happens ...
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7 votes

H-Bridge design understanding

I don't understand why only one of the MOSFETS is being driven with 15V, and the other 12V. That DC-DC converter wasn't included because the high side MOSFET needs 15 V (it does not). The NME1215SC ...
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  • 8,334
7 votes
Accepted

Why does this H-bridge have PWM and Enable pins?

If you don't need the enable pins, there is nothing wrong with tying them high. Just because they are unnecessary in your design, doesn't mean they are in some other design. The purpose of the pin is ...
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6 votes

How does this H-bridge circuit work?

The main problem is that the BD238 is a PNP transisor, not NPN!
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  • 165k
6 votes
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Shunt resistor choice for H-bridge current sensing

Here's the relevant bit of the datasheet: Footnote 2 is "Operational at VREF = 0 to 0.3 V, but accuracy is degraded". This implies you ought to avoid anything that needs a comparison threshold (the ...
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  • 7,639
6 votes

Why do my P-channel MOSFETs keep dying in this H-bridge?

R1 R2 are far too big for all but the smallest nonexistant mosfets.This means that they are turning of much slower than they are turning on .This means that even if you think that you have included ...
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  • 12.4k
6 votes

Is there an ideal PWM frequency for DC brush motors?

I designed and worked on a PWM speed/positional control system that drove 16 brushed DC motors some years back. We were buying from Mabuchi, who sold 350M motors a year at the time. They recommended 2 ...
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  • 17.9k

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