[sdiy] [AH] Re: UA726 clone possible?

[Stewart Pye]

Hi Paul,

Thanks. I'm not sure how the THAT300 is laid out. I guess if pairs of 
transistors were closer to each other than the other transistors then 
you'd use one pair for the expo converter and one for the sensor/heater. 
You certainly wouldn't want to heat one of the expo transistors more 
than the other. I'll see if I can get more info from THAT about how the 
transistors are laid out.


I'm not sure what you mean by "opening the feedback loop on the heater". 
Why would the feedback loop on the heater be open?

Regards,
Stewart.


On 9/12/2015 12:28 PM, Paul Perry wrote:
> When Jim Williams said that it matters (in his version) which
> transistor on the chip did the heating.
> Which is plausible, considering the physics.
> Also I remember someone in EDN magazine saying that opening the
> feedback loop on the
> heater led to oscillations at .01Hz or so... that might led to slow
> troubleshooting..
>
> paul pery Melbourne Australia
>
> ----- Original Message ----- From: "Stewart Pye"
> Sent: Saturday, September 12, 2015 8:21 AM
> Subject: Re: [sdiy] [AH] Re: UA726 clone possible?
>
>
>> Hi Tom,
>>
>> The THAT300 is a 4 NPN transistor array. I think there is also a MAT
>> 4 tranny array that Rick mentioned earlier.
>>
>> I've designed (on paper) a VCO that uses the THAT300 for expo
>> converter with sensor and heater. I'm planning on laying out the PCB
>> this weekend. I probably should breadboard it first, but I like
>> living on the edge! I asked THAT some questions about the maximum
>> dissipation and they were quite helpful. If you're interested I can
>> email the reply to you. Since the max Vce and Vcb voltages are 36V
>> (compared to 15V for the LM3046) you can set it up so you have a
>> higher Vce when the heater is on, so you can dissipate more power
>> with the same current.
>
>