hi friends,
Do you have an idea or circuit for "AC square wave constant voltage generator" with short circuit protection ? The spec: 1. The square wave output is 24v 200mA. 2. Max load's resistance is 8000 ohm 3. When the load's resistance is decreased,the current will drop to a value but the voltage always keep 24v. I have no idea how to keep 24v.
The frequency must be fixed between 100hZ and 100khZ.
I may be being dim here, but ...
Doesn't AC stand for Alternating Current? Which would imply alternating (and therefore not constant) voltage.
A constant voltage would normally be referred to as DC.
"Doesn't AC stand for Alternating Current? Which would imply alternating (and therefore not constant) voltage."
Maybe he means constant amplitude?
I don't think it's unusual to speak of a "constant amplitude" AC source as "constant voltage" - even if, as you say, it isn't literally true?
... we could also ask whether this is really AC - ie alternating - or is it just pulsed DC?
ie, does the voltage swing between +24V and -24V (or +/-12V), or is it just 0V and 24V?
Anyway, you don't specify any load regulation for your generator. If you really did mean that max load is 8000 ohm, then you can select a trivial solution.
Just use a 24V linear voltage regulator and feed the 24V to a switch transistor controlled by a logic-level squarevave generator.
Place a 120 ohm resistor between transistor and connector.
Your short-circuit current will then be 24V/120ohm = 200mA.
Your open-circuit voltage will be 24V (minus a little loss in the switch transistor).
Your fully loaded current will be 24V / (120 + 8000) A = 0.00296A.
Your fully loaded volage will be 24V - 24 * 120 / (120 + 8000) V = 23.65V (minus a little loss in the switch transistor).
Your load regulation will be 1.5% which should be good enough for most usages.
But this is only valid if you by 200mA meant short-circuit current, and didn't mean max current at nominal load (which would be 120 ohm and not 8000 ohm).
Additionally
24 V on 800 ohm get 30 mA so you have to check your specification. For 800 ohm load you need at least a generator with 160 V.
For a simple on/off a switched constant current generator can do the job (the frequency can be the problem if too high).
You are an order of magnitude off. The specified load was 8 kohm, not 800 ohm, so it would take 1,6kV to drive 200mA through the load, and the power sent into the load would be 320W at 50% (?) duty cycle.