My first circuit is a bit advanced (H-bridge!)

Discussion in 'Electronics Homework Help' started by Obit, Jan 25, 2022.

1. Obit

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Jan 19, 2022
Hello, I am teaching myself electronics. I have been reading for several weeks because anybody can build an elementary circuit that turns on an LED, I just kept reading. Electronics is so fascinating and logical, but my simple brain can only handle so much and at last I have become motivated to build an H-bridge with some parts that I have. This is forcing me to confront several problems that likely have easy solutions. This is where my brain starts to fry, please nudge me in the right direction.
I want to operate a small MOTOR (1-6V operation, 3Vfree run Current, 3V 13000RPM free run speed, 3V 800mA stall current)
[1] The first question that comes to mind is, what metrics here are relevant for selecting complimentary transistors and diodes?
The transistors I have on hand are the S8550 and the S8050 (NPN and PNP) these parts arrived in a kit together so I am hoping they work for this. But I am learning so I don't want to build without understanding. TRANSISTORS are (2W, 5Vbase emitter, 20V collector emitter, 30V collector base.)
SO looking at this I am forced to wonder
[2] What metrics here are relevant to the motor and a 9 volt battery and what is not? You see this is a puzzle and the smoke issuing from my ears is my brain on fire, because it gets more complicated then this when I begin to factor in the inductive load to the diodes? [3] What motor metric offered above do I use to determine the proper diode? The diodes I have are IN4007 with a 1A forward current, 30A non-repetitive peak current, 5uA reverse current and a 1000V peak repetitive current
This in a nutshell is my problem; understanding the relationship between these 3 parts regarding their specs. I think I can solve for if I need a resistor: I am using a 9V battery. [4] I figure Once I have my components sorted out I can add up their voltage and subtract from the 9V battery to get the necessary Ohms for my resister?

Last edited by a moderator: Jan 25, 2022
2. Obit

11
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Jan 19, 2022
My motor draw is in Amps and my transistors need to match that, but everything I listed in in Volts. So I have to figure out some Amps.
Also I keep seeing diagrams where the resistors come after the transistors, but that doesnt seem right, because dont I want to protect the transistors from too much current?

3. kellys_eye

4,717
1,312
Jun 25, 2010
They are actually 1W transistors. You need to know the motor current and the Vce(sat) - up to 0.5V on one of the types - to determine the max power dissipated in the transistor when fully saturated (i.e. on).

Back EMF is an issue but the diodes you have will cope more than adequately.

Show us the schematic you intend to use and we can offer more info.

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4. Martaine2005

4,090
1,120
May 12, 2015
You need to learn the basics. Ohms law. V=I/R.

Martin

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5. Audioguru

3,616
763
Sep 24, 2016
You need a 3V to 6V battery that can produce 0.8A to 1.6A.
The little 9V battery cannot produce a current of more than 400mA for a few minutes. The S8050 transistor also cannot produce the high current.

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6. Minder

3,215
700
Apr 24, 2015
I would also look at using Mosfets instead of bi-polar transistors, they are now pretty much the common way for what you are doing.

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7. Bluejets

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Oct 5, 2014
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8. Obit

11
2
Jan 19, 2022
Thankyou. I tried building this circuit with what I have, but it did not work. I individually tested the switches, the motor the battery. I think It will not work for the skepticism offered in a few replies. Either way, I am having fun, but the calculations hurt my brain. Also this circuit didn't use transistors.

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9. Audioguru

3,616
763
Sep 24, 2016
Why do you have switches when you said that PWM pulses are used? The calculations are simple.

You did not show a schematic but I found one for you, I removed its diodes for clarity.
Your breadboard layout does not show a power supply voltage or the PWM pulses voltage.

The pins of your little transistors appear backward and not properly connected to each other and to the motor.
The value of your resistors are way too high.

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