holland
Headphoneus Supremus
- Joined
- Jun 15, 2007
- Posts
- 2,210
- Likes
- 22
I've got a microshar uAmp107B and it runs off 2 1.2V AA NIMH batteries. Here are the things I'm going to change.
- I want to change that to 4 1.2V NIMH AAA batteries, the datasheet seems to indicate better specs at 5V and I don't care about battery life. If it goes from 200 hours to 80hours, that's still more than enough for me.
- May lower gain from 9 to 6.
- Wire in a switch for turn on.
- Change capacitors to Panasonic FM.
The last 3 I've figured out. I need to order stuff for a few Mini3 builds, so it's no issue to add a few more items.
Before I get to my main question. There are some huge caps on the output. A 1000uF with a smaller SMD cap in parallel, before it connects to the output leads and they wire almost directly to the amp chip's output. I'm not sure, yet, if there are any resistors in the line. What is the purpose of this? Bass?
OK, main question. How does NIMH charging work? As far as I can tell there's no regulator, but there are 2 transistors in emitter follower configuration that ties VDD to the Amp chip and to ground.
The amp chips are TPA701, if you look at the datasheet (http://www.ti.com/lit/gpn/tpa701) the NPN transistors (assuming as they are SMD and marked 1P) have their collector connected to the shutdown pin.
Vdd is always supplied to the amp chip and the shutdown pin is used in conjunction with power on and power off. With the audio jacks out, there's no current, so the drops across the voltage drop resistors are negligble.
The base is connected to the voltage source (be it 2.4-2.7V battery or 5V through AC adapter), but through a series of resistors so the voltage drops to 1.2V in 5V DC adapter mode or 1.1V in 2.4-2.7V AA mode).
The emitter is a follower config. 1 transistor's emitter to another's base and the 2nd emitter is to ground. This is directing current around, but is current all that's needed to charge? Is voltage important?
What do you guys use to draw circuit pictures? Any free stuff out there?
Thanks!
- I want to change that to 4 1.2V NIMH AAA batteries, the datasheet seems to indicate better specs at 5V and I don't care about battery life. If it goes from 200 hours to 80hours, that's still more than enough for me.
- May lower gain from 9 to 6.
- Wire in a switch for turn on.
- Change capacitors to Panasonic FM.
The last 3 I've figured out. I need to order stuff for a few Mini3 builds, so it's no issue to add a few more items.
Before I get to my main question. There are some huge caps on the output. A 1000uF with a smaller SMD cap in parallel, before it connects to the output leads and they wire almost directly to the amp chip's output. I'm not sure, yet, if there are any resistors in the line. What is the purpose of this? Bass?
OK, main question. How does NIMH charging work? As far as I can tell there's no regulator, but there are 2 transistors in emitter follower configuration that ties VDD to the Amp chip and to ground.
The amp chips are TPA701, if you look at the datasheet (http://www.ti.com/lit/gpn/tpa701) the NPN transistors (assuming as they are SMD and marked 1P) have their collector connected to the shutdown pin.
Vdd is always supplied to the amp chip and the shutdown pin is used in conjunction with power on and power off. With the audio jacks out, there's no current, so the drops across the voltage drop resistors are negligble.
The base is connected to the voltage source (be it 2.4-2.7V battery or 5V through AC adapter), but through a series of resistors so the voltage drops to 1.2V in 5V DC adapter mode or 1.1V in 2.4-2.7V AA mode).
The emitter is a follower config. 1 transistor's emitter to another's base and the 2nd emitter is to ground. This is directing current around, but is current all that's needed to charge? Is voltage important?
What do you guys use to draw circuit pictures? Any free stuff out there?
Thanks!
